Axonal transport of vasoactive intestinal peptide in sciatic nerve

Dense plexuses of neurones containing immunoreactive vasoactive intestinal peptide (VIP) have been found in discrete areas of the central nervous system and in peripheral organs, including the gastrointestinal tract, pancreas and urogenital system. In many of these locations VIP is concentrated in nerve endings, where it can be released by high K+ concentrations in a Ca2+-dependent manner. VIP release may also be provoked by electrical stimulation of nerves, for example the vagus. VIP thus shows some of the features of neurotransmitter or neuromodulator substances. The presence of immunoreactive VIP in the fine terminal varicosities as well as in the cell bodies of neurones suggests that it might be transported from the perikaryon, where it is presumably formed, to the nerve endings, through the axonal transport system. Such transport would be in keeping with a role for the peptide as a neurohumor or neurohormone. We report here that VIP accumulates in constricted rat sciatic nerves in a manner suggesting fast, anterograde axonal flow.